What is the Posse Comitatus Act regarding military, border?

President Donald Trump will be signing a proclamation directing the departments of Defense and Homeland Security to work together with governors to deploy the National Guard to the southwest border with Mexico. (April 4)
AP

In light of President Trump suggesting Tuesday that the military would be sent to secure the border between Mexico and the United States, U.S. Rep. Mac Thornberry, chairman of the Armed Services Committee, referred to the Posse Comitatus Act that prohibits this action.

“I fully support doing more at the border, but we don’t need to rob the military,” Thornberry, who represents Wichita Falls, said Tuesday during an interview at the Times Record News.

The act, enacted in 1878, prohibits the federal government from using the armed forces for law enforcement except by authorization from Congress.

In United States vs. Yunis, 1988, the court stated: "The Posse Comitatus Act, provides that: Whoever, except in cases and under circumstances expressly authorized by the U.S. Constitution or Act of Congress, willfully uses any part of the Army or the Air Force as a posse comitatus or otherwise to execute the laws shall be fined not more than $10,000 or imprisoned not more than two years, or both.”

A day after making such a suggestion, the White House announced that the president would be signing a proclamation asking governors to work with Homeland Security and the Pentagon to send the National Guard to the border.

Homeland Security Secretary Kirstjen Nielsen said Wednesday that the Trump administration would "work together with our governors to deploy the National Guard to our southwest border to assist the Border Patrol."

"It will take time to have the details in place, but we are beginning today and we are moving quickly," Nielsen was quoted in a USA Today story.

Sen. John Cornyn, R-Texas, said sending the National Guard would be a good idea.

“Utilizing the men and women of the National Guard in a supportive role, as President Obama authorized in 2010, is a commonsense way to temporarily assist law enforcement along the border," Cornyn stated in a press release Wednesday afternoon. "It’s critical that the Administration continue to work in close consultation with state and community leaders to ensure the border region can remain safe and prosperous.”

Kira Innis, of Los Angeles, during rally in support of President Trump a few miles form where President Trump will visit the border wall prototypes near the Otay Mesa Port of Entry in San Diego.
DAVID WALLACE, The Republic via USA TODAY NETWORK

People cheer during rally in support of President Trump a few miles form where President Trump will visits the border wall prototypes near the Otay Mesa Port of Entry in San Diego.
DAVID WALLACE, The Republic via USA TODAY NETWORK

People cheer during rally in support of President Trump a few miles form where President Trump will visits the border wall prototypes near the Otay Mesa Port of Entry in San Diego.
DAVID WALLACE, The Republic via USA TODAY NETWORK

De Le, of San Diego, cheers during a rally in support of President Trump a few miles form where President Trump will visits the border wall prototypes near the Otay Mesa Port of Entry in San Diego.
David Wallace, The Republic via USA TODAY NETWORK

Jacqueline Hackney (left) and her daughter, Tiffany Hackney, 13, (right) both of Corona, Calif., cheer during a rally in support of President Trump a few miles form where he will visit the border wall prototypes near the Otay Mesa Port of Entry in San Diego, Calif., later in the day on March 13, 2018.
David Wallace, The Republic via USA TODAY NETWORK

Lauren Rees holds up a sign during a rally against a scheduled visit by President Trump, March 13, 2018, in San Diego. Protesters chanted, "No ban! No wall!" near the San Ysidro border crossing, where tens of thousands of people enter the U.S. daily from Tijuana, Mexico, many on their way to work or school in San Diego.
Kyusung Gong, AP

Mexican Federal Police cordon off a street directly south of the border wall prototypes in the Magisterial neighborhood of Tijuana, Mexico on on March 12, 2018 ahead of President's Trump's scheduled visit to the area on March 13.
Omar Ornelas, USA TODAY NETWORK

Loree Masonis of Ontario, Calif., cheers during a rally in support of President Trump on March 13, 2018 a few miles form where he will visit the border wall prototypes.
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Greg Brittain of Redland, Calif., is seen during rally in support of President Trump near the Otay Mesa Port of Entry in San Diego, Calif. on March 13, 2018.
David Wallace, The Republic via USA TODAY NETWORK